Armoring of single-conductor electric power cables



Jan. 1, 1929.

E. scHURER ARMORING OF SINGLE CONDUCTOR ELECTRIC POWER CABLES Filed Nov. 1, 1926 I N V EN TOR. Zflzfizmer BY W A TTORNEYS.

Patented Jan. I, 1929.

UNITED STATES PATENT. OFFICE.

EUGEliT SCHIIRER, OF COLOGNE-MULHEIM, GERMANY, ASSIGNOR T FELTEN & GUIL LEAU'ME GABLSWERK ACTIEN-GESELLSCHAFT, 0F COLOGNE-MULHEIM, GERMANY.

ARMORHIG OF SINGLE-CONDUCTOR ELECTRIC POWER CABLES.

Application filed November 1, 1926, Serial No. 145,588, and in Germany October 10, 1925.

I In single conductor electric cables for transmitting heavy currents it has been the usual practice not to use an armoring of iron or steel material so as to prevent the occurrence of losses caused in such /materials through magnetic hysteresis. One means for reducing the losses due to hysteresis consists, as is well-known, in winding a wire armoring on the single conductor cable, in

which the separate wires are separated from one another by for the purpose of opposing a greater resistance to the magnetic induction flux. The gaps between the wires may be filled with anynon-magnetizable material, for instance with an insulating material or with zinc, with which the armoring wires are frequently coated as a protection against rustin IVith the same object the pitches may be increased at the expense of the strength of thc armoring. With these means alone the losses due to the use of ferromagnetic wires have hitherto not been successfully reduced to a reason fractional part of the ohmic losses in the copper conductor, the so-called copper losses. Other armoring materials which are nonmagnetizable are not to be recommended, owing to their high cost.

The present invention provides means which, when used in combination with other precautions referred to above (great, pitch, open armoring) keeps down the losses so as to be sufficiently small, even when ferromagnetic materials are used. The invention lays down a principle, according to which the ferromagnetic materials suitable for the armoring of a single conductor cable may be determined.

The losses caused by the armoring are chief hysteresis losses. If by the precautions escribed steps be taken for keeping the magnetic induction revailingin the armoring wires relatively ow, with all the ferr0magnetic substances the region ofsaturation will never be reached. At low inductions, however, the various substances show a totally different behaviour as regards hysteresis losses than in the region of saturation. Thus, I have found that when open armoringis adopted materials which are preferred in the construction of machines and transformers owing to their low hysteresis losses (for instance various kinds of iron alloyed with silicon) give relatively high losses. These losses are of the same order of magnitude as gaps (open wire armoring),

those of ordinary iron not alloyed with silicon. Alhthese materials have a relatively low coercive force. Conversely it has been found that ferromagnetic materials show lower losses w1th small fields, the greater their coerclve force. By coercive force is to be understood, as usual, the magnetic field strength which mustact for causing the inductlon to disappear after magnetization has been carried to the point of saturation.

The measurement which in practice is the most important in each case is the determinatlon of the additional losses of the armoring, preferably expressed in relation to the socalled copper losses. I obtained the followmg results in single conductor cables with a certain type of wire armoring of different materials and 95 square millimetres cross sectional area for the copper conductor:

Additional losses in the armoring Armoring materlal. g mi dredths o! the coppe losses.

Non-hardenable material: Iron with le tha .2

also alloyed with Si uufflni l to 120% Medium carbon steels (Thomas-Siemens Martin ectrosteel) up to about 0. 7% C 15 to 30% High carbon-steels (above 0. 7% C) "I Under 15% This table shows the dependence of the losses on the carbon content of the armoring material. It is known that the coercive force of steels increases with an increase in the carbon content and reaches its maximum at about 1.5% carbon. On the other hand, steels containing more than 0.9% carbon are already unsuitable for being made into wire, so that the best results are to be obtained Sgt; steel wire having a carbon content of The measurements given above were carrled out with an alternating currenthaving a periodicity of 50 and of 100 to 250 amperes.

It -is known that the coercive force is not only largely dependent onthe chemical admixtures in the iron, but also on the treatment to which it has been subjected (annealing, quenchin drawing, and the like) the favourable loss figures given above relate to steels, in which a high degree of hardness has been obtained in a known manner. When made of such materials. Y

instance from above 900 C., their coercive forces, with a carbon content of 0.2 to 1.5%,

lie between 2 and 12 gauss. When steels having the same carbon content are quenched from about 850 0., the coercive forces lie between 15 and 65 gauss. In materials having a carbon content of from 0.7 to 0.9% I have found armoring losses, when carrying out tests in the above described manner, which amounted to less than 2% of the copper losses. Compared with the above figures the coercive force of selection alloys lies-in the neighbourhood of 1 gauss, and considerably lower values. v In the few cases in which single conductor alternating current cables have been armored with ferromagnetic material, iron or steel has always been used, the carbon content of which did not exceed 0.6%. More par.- ticularly the use of materials of high coercive force has been avoided as far as possible, as there .is a difliculty in dealing with wires In contradistinction to the usual practice it is proposed, according to the present invention, for obtaining lower hysteresis, to use wires made from materials having a high coercive force, for instance steel wires with more than 0.6% carbon content.

In the accompanying drawin Figs. land 2 show a constructional form 0? an armored single conductor alternating current cable according t the present invention longitudinal and transverse section, in which a is the copper conductor built up of single wires, 6 an insulating layer of paper, 0 the lead cover, (1 a layer of padding material, for instance jute, e the armoring wires consisting of a material having a high coercive force, which are kept at a suitable distance apart by paper cords f. In place of the paper cords f wires or cords made of some other non-magnetic material may be .used, or the spaces between the wires may be left vacant.- In cases, where higher armoring losses may be allowed, the armoring of steel .wires may be made with the wires in contact with one another. Over the armoring a layer of padding material 9, for instance jute, may be provided.

WhatIclaim is:

1. An alternating current cable'for transmitting heavy currents, comprising a single core conductor and an armoring of ferromagnetic material force, for the purpose of reducing the armoring losses, as set forth.

2. An alternating current cable for transmitting heavyv currents, comprising a single core conductor and an armoring of hardened carbon steel having a carbon content of between 0.7 to 0.9% and as low a proportion as possible of other admixtures, as set forth.

In testimony whereof I have signed my name to this specification.

EUGEN -scntnrea.

having a high coercive. 

